尝试从MainWindow后台代码绑定到UserControl后台代码时，数据绑定失败

Question

My MainWindow uses the INotifyPropertyChanged interface. I'm using the OnPropertyChanged function that I've been using for a while, which works.
In my MainWindow code-behind I have this:

public ObservableCollection<bool> MwOc { get; set; }

private bool _mwBool;
public bool MwBool { get { return _mwBool; } set { _mwBool = value; OnPropertyChanged(); } }

public MainWindow()
{
    InitializeComponent();

    MwOc = new ObservableCollection<bool>();

    MwOc.Add(false);
    MwBool = true;

    Console.WriteLine("MwOc:   " + MwOc.Count);
    Console.WriteLine("MwBool: " + MwBool);

    DataContext = this;
}

All my MainWindow xaml does is this:

<local:UserControl1 x:Name="Control" UcOc="{Binding MwOc}" UcBool="{Binding MwBool}" />

My UserControl has two dependency properties: UcOc an ObservableCollection<bool> and UcBool a bool
Here is my UserControl code:

public ObservableCollection<bool> UcOc
{
    get { return (ObservableCollection<bool>)GetValue(UcOcProperty); }
    set { SetValue(UcOcProperty, value); }
}

public static readonly DependencyProperty UcOcProperty =
DependencyProperty.Register("UcOc", typeof(ObservableCollection<bool>), typeof(UserControl1));

public bool UcBool
{
    get { return (bool)GetValue(UcBoolProperty); }
    set { SetValue(UcBoolProperty, value); }
}

public static readonly DependencyProperty UcBoolProperty =
    DependencyProperty.Register("UcBool", typeof(bool), typeof(UserControl1));

public UserControl1()
{
    InitializeComponent();
    UcOc = UcOc ?? new ObservableCollection<bool>();

    DataContextChanged += (o, e) => { Console.WriteLine("DataContextChanged"); Print(); };
}

public void Print()
{
    UcOc = UcOc ?? new ObservableCollection<bool>();
    Console.WriteLine("UcOc:   " + UcOc.Count);
    Console.WriteLine("UcBool: " + UcBool);
}

My UserControl xaml is empty (just has the default <Grid></Grid> )

The output of this program is

MwOc:   1
MwBool: True
DataContextChanged
UcOc:   0
UcBool: False

How should I update the UserControl properties when its DataContext changes?

Answer 1

In the MainWindow xaml, the bindings need the NotifyOnTargetUpdated property set to true.
Instead of:

<local:UserControl1 x:Name="Control" UcOc="{Binding MwOc}" UcBool="{Binding MwBool}" />

use:

<local:UserControl1 x:Name="Control" UcOc="{Binding MwOc, NotifyOnTargetUpdated=true}" UcBool="{Binding MwBool, NotifyOnTargetUpdated=true}" />

In the UserControl, subscribing to the DataContextChanged event also causes the binding to fail on the ObservableCollection<bool> but not the bool . For currently unknown reasons.